The present invention relates to a fuel system as well as a method for controlling the same. More specifically, it relates to a fuel system of motor vehicles adapted to be powered by alcohol-containing fuels, comprising a main tank for fuel, a cold-start tank for fuel which is sufficiently inflammable to be used in connection with cold starts, as well as a fuel line system connecting these tanks to each other and to injection means of the engine of the vehicle, at least one pump being adapted to transfer fuel through the fuel line system.
Today, many vehicles are adapted to be powered by alcohol-containing fuels as well as by petrol, so-called Flexible Fuel Vehicles (FFV). These vehicles can be powered by fuels with varying alcohol content, as well as by pure petrol. Common alcohol mixtures are, for example, M85, i.e. 85% methanol, and E85, i.e. 85% ethanol, in which, accordingly, the petrol content is about 15%. However, one problem associated with the use of high alcohol-content fuels is that the vehicle is difficult to start, especially when it is cold. If the temperature is below about xe2x88x9210xc2x0 C., the alcohol does not vaporise at all.
One way of overcoming this problem is to have a separate cold-start tank with petrol, which is used when starting the engine. Subsequently, when the engine has started and is beginning to warm up, the main tank with the alcohol-containing fuel is connected instead. Such a fuel system is described in, for example. U.S. Pat. No. 4,911,116.
However, one problem associated with this known system is that in this connection two tanks must be filled separately. Consequently, the driver must keep track of the level in both tanks in order to be able to fill them in time. Moreover, he must differentiate between two separate filler tubes. In addition to the fact that the driver may find this complicated and troublesome, there is also a risk that the driver will fill the cold-start tank with alcohol-containing fuels by mistake, thus making the vehicle difficult to start.
Consequently, it is an object of the present invention to provide a fuel system as well as a method for controlling the same in which the above-mentioned drawbacks of the prior art are obviated.
An important advantage of the device according to the invention is that all refilling of fuel can be carried out into the main tank, which is easier for the driver. Subsequently, the fuel system automatically transfers fuel from the main tank to the cold-start tank when the conditions are suitable for such a transfer. Furthermore, in this way, fewer filler tubes are required than in prior art devices, contributing to increased safety, particularly with respect to the risk of fire in connection with a side collision. Many other features and advantages are also provided by the invention, as will be apparent from the following description of a preferred embodiment.